Incandescent electric lamp



(No Model.)

T. 'A. EDISON.

INGANDESGENT ELECTRIC LAMP.

No. 274,295. Patented Mar.20, 1883.

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iv UNITED STATES PATENT Erica.

THOMAS A. EDISON, OF MENLO PARK, NEW JERSEY.

-INC ANDESCENT ELECTRIC LAMP.

SPECIFICATION forming part of Letters Patent No. 274,295, dated March .20, 1883.

i Application filed November 23, 1882. (No DlOdGlr) To all whom it may concern:

Be itknown that I, THOMAS A. EDISON, of Menlo Park, in the county of Middlesex and State of New Jersey, have invented a new and useful Improvement in Incandescing Electric Lamps, (Case No. 516,) of which the following is a specification.

This invention relates to incandescing electric lamps, wherein flexible filaments of carbon are inclosed in hermetically'sealed chambers made entirely of glass, with leading-in wires passing through and sealed into the glass; and the object of the invention isprincipally to lengthen the life of electric lamps of this character by diminishing the electrical carrying be- V tween the flexible carbon filament and the inclosing-chamber, or the metallic terminals of the filamentwithin the lamp, and incidentally to increase the resistance of the lamp, so as to reduce the investment required for conductors.

Heretofore in electric lamps of this character,

. and without diminishing in the least thedegree of vacuum; but I find that advance in this direction is limited by reason of the increased deposit of the carbon upon the walls of the glass chamber,obscuringthe light and diminishing considerably the exterior candle-power of the lamp, and also consuming and destroy ing the fine filament, reducing materially the f length of life of the lamp.

I have found that the amount of deposit in any given period depends generally upon the degree of ineandescence per unit surface to which the carbon filament is raised, the higher the degree of incandescence the more rapid being the deposit. It also depends upon the state of the vacuum, the higher the vacuum the greater being the deposit. l his deposit I I have discovered is due to electrical carrying of the carbon of the filament, the phenomenon being similar to that which takes place in the well-known Geissler tubes, wherein at certain I have also discovered that the economy of the carbon-filament lamp (the number of stand ard lamps per horse-power) increases as the pressure within the globe diminishes, up to a certain stage of the vacuum, when any higher exhaustion does not practically increase the economy. It the vacuum is diminished below this point of greatest economy to prevent electrical carrying, the economy of the lamp is diminished, since the residual air acts as a carrier of heat to the walls of the chamber,'where it is rapidly dissipated; but, owing to the greatly diminished electrical carrying of the carbon from the filamentwhenthe vacuumislow,Iain enabled to diminish the radiating-surface, so as to raise each unitot' surface to a higher degree of incandescence than would be practicable were the vacuum higher and the electrical carrying um and high incandescence and resistance will a have a longer life than if the vacuum were higher, and its candle-power will not be diminished by the obscuration of the globe by a deposit of carbon. It will also permit of a reduction in the size of conductors for carrying the current to and from-the lamps by reason of its increased resistance, and the filament itself willbe more flexible and less liable to break. 7

In carrying out the invention the flexible carbon filament. is produced by the carbonizareduced to an amorphous or semi-amorphous condition in the way now well understood.

-The filament before carbonization, however,

may be reduced to a smaller cross-section than usual heretofore, in order to produce the reduction of radiating-surface and increase of re-' sistance per unit of radiating-surface necessary to compensate for the loss caused by the reduced vacuum. For illustration, it may be stated that the radiating-surface can be reduced in size two-tenths; but the sizes of filaments used by me at present may be retained, the loss in economy being more than counterbalanced by the increased length of life. The flexible carbon filament is secured to the leading-in wires, which are sealed in one glass part of the lamp, and this part is fused to the glass globe of the lamp in the usual or any suitable way. Thelampis then connected with a Sprengel pump, andthe globe exhausted until a high vacuum is obtained,so as to remove all oxygen from the globe. During the latter part of the operation of exhausting the lamp the flexible carbon filament may be gradually raised to an incandescence higher than that at which itis intended afterward to be used; butthis heating of the filament may be omitted. After the exhaustion of the lamp-globe is completed an inert gas is allowed to pass into the globe, gradually reducing the vacuum and increasing the pressure within the globe. This is preferably done by providing the pump with a tube containing a solid substance, which, when heated, will evolve an inert gas. The heat is applied at the proper time to the exterior of the tube containing the substance. The flexible carbon filament is raised to incandescence during the time that the inert gas is being admitted into the lamp-globe and certain phenomena will be noticed during this period. As the pressure gradually increases a light-blue halo very much spread out will appear upon the positive clamp of the filament. As more gas passesin, the halo will increase in density and hug the clamp. At this pressure carbon from the filament is deposited on the clamp in considerable quantity, which is due to the increase of the electrical resistance ot'the vacuum and the consequent prevention of deposit upon the globe. If, now, the pressure be further increased, the blue halo leaves the metallic portions of the clamp and appears on the carbon at the 5 juncture of the latter and the metal of the the inert gas this pressure may be when a mercurial column connected with the lamp stands at a heightot' about twenty inches; but

with hydrochloric-acid gas, on account of its greater electrical resistance, the pressure may be somewhat reduced. At twenty-nine inches with nitrogen and equivalent pressure with other gasses the electrical carrying is greatly diminished. This vacuum of twenty nine inches or below that height for nitrogen and equivalent pressures with other gases is what I hereinafter term a low vacuum.

Since the blue halo in the lamp disappears altogether to the eye when a certain pressure is reached, on account of the incandescence of the filament, and since the operation should be carried beyond this point, a Geissler sparkgage may be used to determine the exact point to seal off the lamp, the terminals of the Geissler spark-gage being connected to an induction-coil worked by a constant battery. A mercurial column may be used for the purpose; but the Geissler spark-gage is preferred, for the reason that the electrical carrying depends, where the vacuum is low, both upon the nature of the residual gas and the pressure, which conditions will also affect the Geissler spark-gage, in which the phenomena due to electrical carrying can be observed after their disappearance to the eye in the lamp, while the mercurial column is only affected by the pressure.

The different degrees of exhaustion at which certain phenomena will appear in the sparkgagedepend upon the size and distance apart of the electrodes, as well as on the chamber of the gage and on the electro-motive force of the coil; hence it is necessary to determine, in the first instance, by the disappearance of the blue halo from the clamps 'ot' the filament, due to increased pressure, the appearance of the spark-gage at the exact moment when thelamp is to be sealed off, which is anincreased pressure of several inches of a column of mercury after the disappearance of the halo from the metallic terminals of the filament. The residual gas might be allowed to flow in until the gas within the globe is at atmospheric pressure, and good-results would be obtained as far as the electrical carrying is concerned; but the economy would be considerably diminished without a corresponding increase of the life of the filament hence it is best to diminish the pressure for the sake of economy, but not to the point where the blue halo begins to appear on the metallic terminals of the filament.

Instead of exhaustin g, to a high vacuum with a moron ry-pnm p, and then gradually reducing the vacuum to the proper point by means of an inert gas, the lamp is first exhausted to a high vacuum, and the inert gas is then allowed to flow into the lamp until the vacuum is reduced IIO to atmospheric pressure, when the inert gas is obtained; or any other way of displacing the oxygen by an inert gas and obtaining the desired pressure may be employed.

The makingoftheinclosing-chamberentirely of glass, through which the leading-in wires are passed and in which they are sealed, and the hermetical closing of such glass inclosingchamber, assure the retention of the same con- .ors having, like carbon, a high specific resist- In the accompanying drawings, Figure 1 is.

a view of the lamp; Fig. 2, an elevation showing the principalparts of the pump and the devices connected therewith. Figs. 3, 4, and 5 illustrate the phenomena that appear at the positive clamp of the filament, and Figs. 6, 7,. 8. 9, and 10 illustrate the phenomena thatap pear in the Geissler'spa'rk-gage;

, A is the glass lamp-globe, fused to the inside glass part, B, through which pass the leading-in wires 1 2, such wires being sealed into the upper end of B by the fusion of the glass around and upon them.

0 is the flexible carbon filament, secured to the leading-in wires in any suitable way. The globe A is provided with an inert gasat a low vacuum or atmospheric pressure, as before described, and is sealed at a.

D is the Sprengel pump, the mercury entering at b and passing out at c. i

E is a Geissler spark-gage, connected with the exhaust-tube of the pump. lts terminals are connected with an induction-coil, F,worked by a constant battery, G. l

H is a chamberlor tube, also connected with the exhaust-tube ofthe pump. The tube H contains the solid. material for producing the inert gas when the tube is heated. i This material maybe, for illustration, solid cyanide of mercury, which evolves cyanogenywhen heated. Otherinert gases may, however, be used, being evolved from the decomposition of different salts by heat. The exhaust-tube may be connected with a reservoir of pure inert gas which can be allowed to pass, as desired, into the vacuum by means of a stop-cock; but the method first described is preferred, since it is quite impracticable to manipulate thegas or make it free from oxygen. This difficulty is not met'with when the gas is evolved from a solid in a tube by the application of heat to the exterior of the tube, and the heat can be so applied as to set free the exact quantity of gas desired, the quantity being regulated with 'a nicety and exactness which cannot be obtained with a stop-cock.

Iis a chamber or tube containing a drying agent.

Figs. 3, 4.. and 5 represent the appearance of the blue halo on the positive clamp at three stages; Fig. 3, when it first appears, which corresponds with nitrogen for the inert gas,to a pressure shown in the mercury column of thirty and three-sixteenthsiuches; Fig.4,when it becomes dense and hugs the clamp, which occurs at a pressure of twenty-nine and ninesixteenths inches; and Fig. 5, when it is about to disappear, which occurs at a pressure of twenty-eight and fifteen-sixteenths inches. Figs. 6, 7, 8, 9, and 10 represent the phenomena of the spark-gage. Fig. 6 shows the spark between the terminals at the atmospheric pressure. the positive pole, which occurs at twenty Fig. 7 shows a halo on the end of l inches. Figs. 8 and 9 show it extending along chamber or the metallic terminals of the filament within the lamp is prevented, substantially as set forth.

2. An incandescing electric'lamp having, in combination, a flexible carbon filament, a hermetically-sealed inclosing-chamber made entirel y of glass,leading-in wires passingthrough and sealed into the glass, and an inert gas having the definite high pressure described, for the purpose set forth.

3. The method of completing incandescing electric lamps having flexible carbon filaments andinclosing-chambers entirely of glass, consisting in exhausting the inclosing-chamhers until a high vacuum is obtained for removing the oxygen, then filling the chambers with an inert gas at apressure sufficiently high to cause the disappearance of the blue halo from the positive clamp of the filament, and. then hermetically sealing the chambers by a fusion of the glass, substantially as set forth. 4. The method of completingincandescing electric lamps having flexible carbon filaments and in closiu g-cham hers entirely of glass, consisting in exhausting the inclosing-chambers until a high vacuum is obtained for removing the oxygen, then raising the filaments to incandescence, then filling the chambers with an inert gas at a pressure sufficiently high to cause the disappearance of the blue halo fromthe positive clamp of the filament, and I then hermetically sealing the chambers by a fusion of the glass while the filaments are incandescent, substantially as set forth.

5. The method of completing incandescing I off said lamp from connection with said chamelectric lamps, consisting in exhausting the her and the exhausting apparatus, substanlamp,and at the same time exhausting a chamtially as set forth. a ber connected with said lamp, and containing This, specification signed and witnessed this 5 a material evolving an inert gas when heated, 14th day of November, 1882.

then heating such chamber externallyto evolve the gas,then filling the lamp with the inert I THOS' EDISON" gas at a pressure sufficiently high to cause the WVitnesses: disappearance of the blue halo from the posi- WM. H. 'MEADOWGROFT,

1o vLive clamp of the filament, and then sealing EDWARD H. PYATT. 

